Image sensing apparatus, imaging system, and image sensing apparatus driving method

ABSTRACT

An image sensing apparatus includes a pixel array including an optical black region and effective pixel region, and a scanning unit which scans the pixel array. The scanning unit includes a first shift register which scans the optical black region by a shift operation, and a second shift register which scans the effective pixel region by a shift operation. The second shift register starts the shift operation during a first period when the first shift register scans the optical black region, and scans a readout region serving as a partial region of the effective pixel region during a second period following the first period.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image sensing apparatus, imagingsystem, and image sensing apparatus driving method.

2. Description of the Related Art

Previously proposed conventional image sensing apparatus has a pixelarray including an optical black region and effective pixel region (seeJapanese Patent Laid-Open No. 2001-45383). According to the techniquedisclosed in Japanese Patent Laid-Open No. 2001-45383, a shift registerfor scanning the respective rows or columns of the pixel array is formedfrom a plurality of circuit blocks. A decoder circuit for selecting oneof the circuit blocks is arranged on the input side of the shiftregister. By selecting a circuit block by the decoder circuit, scanningof pixels can start for each pixel block including a plurality of pixelsin an effective pixel region.

Recently, image sensing apparatuses such as a video camera and stillcamera require a high-precision electronic anti-shake (camera shakecorrection) function. As a technique for implementing the electronicanti-shake function, the present inventor has examined to shift areadout region, which is a partial region of the effective pixel region,in the direction of camera shake in the effective pixel region. To shiftthe readout region in the effective pixel region in order to implementthe electronic anti-shake function, the readout start position of thereadout region is changed for each pixel (for each row and each column)in the effective pixel region.

According to the technique in Japanese Patent Laid-Open No. 2001-45383,when the readout start position does not exist at the end of a pixelblock, pixels are sequentially skipped from a pixel at the end of apredetermined pixel block to that at the readout start position afterthe end of scanning the optical black region. This may prolong theperiod until scanning of the readout region starts for each pixel in theeffective pixel region after the end of scanning the optical blackregion.

If a decoder circuit for selecting one of flip-flops which build theshift register is arranged on the input side of the shift register inorder to scan the pixel array, the readout start position of the readoutregion can be changed for each pixel in the effective pixel region. Inthis case, however, the size of a circuit for scanning the pixel arraymay become large, complicating the arrangement of the image sensingapparatus.

SUMMARY OF THE INVENTION

The present invention provides an image sensing apparatus, imagingsystem, and image sensing apparatus driving method capable ofshortening, by a simple arrangement, the period until scanning of thereadout region starts for each pixel in the effective pixel region afterthe end of scanning the optical black region.

According to the first aspect of the present invention, there isprovided an image sensing apparatus comprising: a pixel array includingan optical black region and an effective pixel region; and a scanningunit which scans the pixel array, the scanning unit including: a firstshift register which scans the optical black region by a shiftoperation; and a second shift register which scans the effective pixelregion by a shift operation, wherein the second shift register startsthe shift operation during a first period when the first shift registerscans the optical black region, and scans a readout region serving as apartial region of the effective pixel region during a second periodfollowing the first period.

According to the second aspect of the present invention, there isprovided an image sensing apparatus comprising: a pixel array includingan optical black region and an effective pixel region; and a scanningunit which scans the pixel array, the scanning unit including: a firstshift register which scans the optical black region by a shiftoperation; and a second shift register which scans the effective pixelregion by a shift operation, wherein the second shift register includesa plurality of circuit blocks which receive a second start signal andscan the effective pixel region for each pixel block including aplurality of pixels, and the second shift register selects one of theplurality of circuit blocks and causes the selected circuit block tostart the shift operation during a first period when the first shiftregister scans the optical black region, and causes the selected circuitblock to start scanning a readout region serving as a partial region ofthe effective pixel region during a second period following the firstperiod.

According to the third aspect of the present invention, there isprovided an imaging system comprising: an image sensing apparatusdefined as the first or second aspect of the present invention; anoptical system which forms an image on an image sensing plane of theimage sensing apparatus; and a signal processing unit which processes asignal output from the image sensing apparatus to generate image data.

According to the fourth aspect of the present invention, there isprovided a method of driving an image sensing apparatus having a pixelarray including an optical black region and an effective pixel region,and a scanning unit including a first shift register which receives afirst start signal and scans the optical black region by a shiftoperation of the first start signal, and a second shift register whichreceives a second start signal and scans the effective pixel region by ashift operation of the second start signal, the method comprising: afirst step of causing the first shift register to scan the optical blackregion during a first period; a second step of causing the second shiftregister to start the shift operation during the first period; and athird step of causing the second shift register to scan a readout regionserving as a partial region of the effective pixel region during asecond period following the first period.

According to the fifth aspect of the present invention, there isprovided a method of driving an image sensing apparatus having a pixelarray including an optical black region and an effective pixel region,and a scanning unit including a first shift register which scans theoptical black region by a shift operation, and a second shift registerwhich scans the effective pixel region by a shift operation, the secondshift register including a plurality of circuit blocks which receive asecond start signal and scan the effective pixel region for each pixelblock including a plurality of pixels, the method comprising: a firststep of causing the first shift register to scan the optical blackregion during a first period; a second step of causing the second shiftregister to select one of the plurality of circuit blocks and cause theselected circuit block to start the shift operation during the firstperiod; and a third step of causing the second shift register to causethe selected circuit block to start scanning a readout region serving asa partial region of the effective pixel region during a second periodfollowing the first period.

The present invention can shorten the period until scanning of thereadout region starts, for each pixel in the effective pixel regionafter the end of scanning the optical black region.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the arrangement of an image sensing apparatus 100according to the first embodiment of the present invention;

FIG. 2 is a view for explaining a readout region RR1 in an effectivepixel region 03;

FIG. 3 is a circuit diagram of a horizontal shift register unit;

FIG. 4 is a timing chart showing the detailed operation of a scanningunit 30;

FIG. 5 is a block diagram of an imaging system to which the imagesensing apparatus according to the first embodiment is applied;

FIG. 6 is a view of the arrangement of an image sensing apparatus 200according to the second embodiment of the present invention;

FIG. 7 is a view for explaining a readout region RR201 in an effectivepixel region 03;

FIG. 8 is a circuit diagram of a horizontal shift register unit; and

FIG. 9 is a timing chart showing the detailed operation of a scanningunit 230.

DESCRIPTION OF THE EMBODIMENTS

The schematic arrangement and schematic operation of an image sensingapparatus 100 according to the first embodiment of the present inventionwill be described with reference to FIG. 1. FIG. 1 is a view of thearrangement of the image sensing apparatus 100 according to the firstembodiment of the present invention.

The image sensing apparatus 100 comprises a pixel array 10 and scanningunit 30.

The pixel array 10 has an optical black (to be referred to as OBhereinafter) region 02 and an effective pixel region 03.

The OB region 02 is shielded from light, and includes a plurality ofelements for reading out a reference signal for the black level. The OBregion 02 is formed by three columns from the left end or three rowsfrom the upper end of the pixel array 10. The element can be one whichhas the same structure as that of an effective pixel and is shieldedfrom light. Alternatively, the element is one which does not have aregion corresponding to the photoelectric conversion unit (e.g.,photodiode) of an effective pixel or has a small volume of a regionwhere the signal charges of the photodiode are stored.

The effective pixel region 03 includes a plurality of pixels whichreceive light corresponding to the optical image of an object and fromwhich a pixel signal obtained by photoelectrically converting the lightis read out. The effective pixel region 03 is a region of 9 rows×9columns from the lower and right ends of the pixel array 10.

The scanning unit 30 scans the pixel array 10 to drive respectivepixels. The scanning unit 30 includes a horizontal shift register unit04 and vertical shift register unit 07. The horizontal shift registerunit 04 horizontally scans the respective columns of the pixel array 10.The vertical shift register unit 07 vertically scans the respective rowsof the pixel array 10.

The horizontal shift register unit 04 includes a first horizontalscanning circuit 05 and second horizontal scanning circuit 06. Inaccordance with horizontal scan signals hob1 to hob3, the firsthorizontal scanning circuit 05 sequentially scans the respective columnsof a region extending in the vertical direction in the OB region 02. Thesecond horizontal scanning circuit 06 sequentially scans the respectivecolumns of the effective pixel region 03 in accordance with horizontalscan signals h1 to h9.

The first horizontal scanning circuit 05 and second horizontal scanningcircuit 06 commonly receive a clock signal HCLK and reset signal hrst.The first horizontal scanning circuit 05 and second horizontal scanningcircuit 06 receive a first start signal hst_ob and second start signalhst, respectively. The second horizontal scanning circuit 06 receives anend notification signal e_ob from the first horizontal scanning circuit05. Since two start signals (start pulses) are respectively used for thefirst horizontal scanning circuit 05 and second horizontal scanningcircuit 06, the OB region 02 and effective pixel region 03 can beindependently scanned.

The vertical shift register unit 07 includes a first vertical scanningcircuit 08 and second vertical scanning circuit 09. In accordance withvertical scan signals vob1 to vob3, the first vertical scanning circuit08 sequentially scans the respective rows of a region extending in thehorizontal direction in the OB region 02. The second vertical scanningcircuit 09 sequentially scans the respective rows of the effective pixelregion 03 in accordance with vertical scan signals v1 to v9.

The first vertical scanning circuit 08 and second vertical scanningcircuit 09 commonly receive a clock signal VCLK and reset signal vrst.The first vertical scanning circuit 08 and second vertical scanningcircuit 09 receive a start signal (first start signal) vst_ob and startsignal (second start signal) vst, respectively. The second verticalscanning circuit 09 receives an end notification signal e_ob from thefirst vertical scanning circuit 08. Since two start signals (startpulses) are respectively used for the first vertical scanning circuit 08and second vertical scanning circuit 09, the OB region 02 and effectivepixel region 03 can be independently scanned.

The arrangement and operation of the scanning unit 30 will be explainedwith reference to FIGS. 2 and 3. FIG. 2 is a view for explaining areadout region RR1 in the effective pixel region 03. FIG. 3 is a circuitdiagram of the horizontal shift register unit. Although the horizontalshift register unit 04 will be mainly explained, the followingdescription also applies to the vertical shift register unit 07.

As described above, the horizontal shift register unit 04 includes thefirst horizontal scanning circuit 05 and second horizontal scanningcircuit 06.

The first horizontal scanning circuit 05 includes a first shift register31. The first shift register 31 includes a plurality of flip-flops 11 to14. The first shift register 31 receives the first start signal hst_ob,clock signal HCLK, and reset signal hrst via an input terminal D, clockterminal C, and reset terminal R of each flip-flop, respectively. Uponreceiving the reset signal hrst, the first shift register 31 is reset insynchronism with the clock signal HCLK. An output terminal Q of each ofthe flip-flops 11 to 14 is connected to pixels on each column of aregion RR2 extending in the vertical direction in the OB region 02. Uponreceiving the first start signal hst_ob, the first shift register 31shifts the first start signal hst_ob in synchronism with the clocksignal HCLK, sequentially scanning the respective columns of the regionRR2 extending in the vertical direction in the OB region 02. That is,the first shift register 31 supplies the horizontal scan signals hob1 tohob3 to the respective columns of the pixel array 10.

After the end of scanning the OB region 02, the first shift register 31outputs the end notification signal e_ob to an enable circuit 20 (to bedescribed later). That is, upon completion of scanning the OB region 02,the first shift register 31 controls the enable circuit 20 to enable aplurality of signal lines SL1, SL2, SL3, . . . .

The second horizontal scanning circuit 06 includes a second shiftregister 32, the plurality of signal lines SL1, SL2, SL3, . . . , andthe enable circuit 20.

The second shift register 32 includes a plurality of flip-flops (e.g., Dflip-flops) 15, 16, 17, 18, . . . . The second shift register 32receives the second start signal hst, clock signal HCLK, and resetsignal hrst via the input terminal D, clock terminal C, and resetterminal R of each flip-flop, respectively. Upon receiving the resetsignal hrst, the second shift register 32 is reset in synchronism withthe clock signal HCLK.

The plurality of signal lines SL1, SL2, SL3, . . . connect the secondshift register 32 to the pixel array 10. That is, the output terminal ofeach of the flop-flops 15, 16, 17, 18, . . . is connected to pixels oneach column of the effective pixel region 03. Note that the second shiftregister 32 includes flip-flops by the number of columns of theeffective pixel region 03, which is not shown in FIG. 3.

Upon receiving the second start signal hst, the second shift register 32shifts the second start signal hst in synchronism with the clock signalHCLK, sequentially scanning the respective columns of the effectivepixel region 03.

Upon receiving the end notification signal e_ob, the enable circuit 20enables a signal output from the second shift register 32. An outputline SLE of the enable circuit 20 and the plurality of signal lines SL1,SL2, SL3, . . . are connected to the respective columns of the pixelarray 10 via AND gates.

More specifically, the enable circuit 20 outputs an inactive enablesignal EN (e.g., an L-level signal) to the output line SLE until itreceives the end notification signal e_ob after it is reset by the resetsignal hrst. The enable circuit 20 disables the plurality of signallines SL1, SL2, SL3, . . . during a first period TP1 (see FIG. 4) whenthe first shift register 31 scans the OB region 02.

Upon receiving the end notification signal e_ob, the enable circuit 20outputs an active enable signal EN (e.g., an H-level signal) to theoutput line SLE. The enable circuit 20 receives the end notificationsignal e_ob to enable the plurality of signal lines SL1, SL2, SL3, . . .during a second period TP2 (see FIG. 4) following the first period TP1.

As a result, the second shift register 32 starts shifting the secondstart signal hst during the first period TP1 (starts the shiftoperation), and scans the readout region RR1 serving as a partial regionof the effective pixel region 03 during the second period TP2.

The second shift register 32 may also include a plurality of clockedinverters instead of a plurality of flip-flops.

The detailed operation of the scanning unit 30 will be explained withreference to FIG. 4. FIG. 4 is a timing chart showing the detailedoperation of the scanning unit 30.

In FIG. 4, the first period TP1 is a period when the first shiftregister 31 scans the OB region 02. The second period TP2 follows thefirst period TP1.

At timing T1 (first step), the first start signal hst_ob is inputexternally (from a timing generator 98 to be described later) to thefirst horizontal scanning circuit 05. Upon receiving the first startsignal hst_ob, the first shift register 31 starts scanning the regionRR2 extending in the vertical direction in the OB region 02. From thistiming, the first period TP1 starts.

At timing T2 (second step), the first shift register 31 shifts the firststart signal hst_ob by one stage to activate the horizontal scan signalhob1 corresponding to the first column of the OB region 02. At the sametime, the second start signal hst is externally input to the secondhorizontal scanning circuit 06. Upon receiving the second start signalhst, the second shift register 32 starts shifting the second startsignal hst (starts the shift operation). At this time, the enablecircuit 20 has not received the end notification signal e_ob yet, andthus keeps the plurality of signal lines SL1, SL2, SL3, . . . disabled.

At timing T3, the first shift register 31 shifts the first start signalhst_ob by one stage to activate the horizontal scan signal hob2corresponding to the second column of the OB region 02. At the sametime, the second shift register 32 shifts the second start signal hst byone stage. At this time, even if an output from the first stage of thesecond shift register 32 is active (as indicated by a broken line), theenable circuit 20 keeps the plurality of signal lines SL1, SL2, SL3, . .. disabled, so the horizontal scan signal hi corresponding to the firstcolumn of the effective pixel region 03 does not become active. That is,the second shift register 32 skips the first column of the effectivepixel region 03.

At timing T4, the first shift register 31 shifts the first start signalhst_ob by one stage to activate the horizontal scan signal hob3corresponding to the third column of the OB region 02. At the same time,the second shift register 32 shifts the second start signal hst by onestage. At this time, even if an output from the second stage of thesecond shift register 32 is active (as indicated by a broken line), theenable circuit 20 keeps the plurality of signal lines SL1, SL2, SL3, . .. disabled, so the horizontal scan signal h2 corresponding to the secondcolumn of the effective pixel region 03 does not become active. That is,the second shift register 32 skips the second column of the effectivepixel region 03.

At timing T5 (third step), the first shift register 31 shifts the firststart signal hst_ob by one stage to output the end notification signale_ob to the enable circuit 20. That is, the first shift register 31controls the enable circuit 20 to enable the plurality of signal linesSL1, SL2, SL3, . . . in response to the end of scanning the OB region02. Upon receiving the end notification signal e_ob, the enable circuit20 outputs an active enable signal EN (e.g., an H-level signal) to theoutput line SLE. The enable circuit 20 enables the plurality of signallines SL1, SL2, LS3, . . . . At this time, the second shift register 32shifts the second start signal hst by one stage. At this time, since anoutput from the third stage of the second shift register 32 is activeand the enable circuit 20 has enabled the plurality of signal lines SL1,SL2, SL3, . . . , the horizontal scan signal h3 corresponding to thethird column of the effective pixel region 03 becomes active. In otherwords, the second shift register 32 starts scanning the readout regionRR1 in the effective pixel region 03. The first period TP1 ends at thistiming, and the second period TP2 starts from this timing.

At timing T6, the second shift register 32 shifts the second startsignal hst by one stage. At this time, since an output from the fourthstage of the second shift register 32 is active and the enable circuit20 has enabled the plurality of signal lines SL1, SL2, SL3, . . . , thehorizontal scan signal h4 corresponding to the fourth column of theeffective pixel region 03 becomes active. That is, the second shiftregister 32 scans the readout region RR1 in the effective pixel region03.

In the same way, the second shift register 32 sequentially activates thehorizontal scan signals h5 to h8 to sequentially scan the respectivecolumns (columns subjected to readout) of the readout region RR1.

At timing T7, the first shift register 31, second shift register 32, andenable circuit 20 receive an active reset signal hrst and are reset.Upon the reset, the second shift register 32 ends the shift operation ofthe second start signal hst. Upon the reset, the enable circuit 20outputs an inactive enable signal EN (e.g., an L-level signal) to theoutput line SLE again. The enable circuit 20 disables the plurality ofsignal lines SL1, SL2, SL3, . . . . That is, the horizontal scan signalh9 corresponding to the ninth column of the effective pixel region 03becomes inactive, and the second shift register 32 ends scanning thereadout region RR1.

As described above, the second shift register 32 receives the secondstart signal hst in the first period TP1 at a timing (e.g., timing T2shown in FIG. 4) to start scanning the readout region RR1 from the startof the second period TP2. Even if a decoder circuit for selecting one offlip-flops which build the shift register is not arranged, the perioduntil scanning of the readout region RR1 starts for each pixel in theeffective pixel region 03 after the end of scanning the OB region 02 canbe shortened. Hence, the period until scanning of the readout regionstarts for each pixel in the effective pixel region after the end ofscanning the optical black region can be shortened by a simplearrangement.

FIG. 5 shows an example of an imaging system to which the image sensingapparatus according to the present invention is applied.

As shown in FIG. 5, an imaging system 90 mainly comprises an opticalsystem, the image sensing apparatus 100, and a signal processing unit.The optical system mainly comprises a shutter 91, lens 92, and stop 93.The signal processing unit mainly comprises a sensed signal processingcircuit 95, an A/D converter 96, an image signal processor 97, a memory87, an external I/F 89, the timing generator 98, an overallcontrol/arithmetic unit 99, a recording medium 88, and a recordingmedium control I/F 94. The signal processing unit may not comprise therecording medium 88.

The shutter 91 is arranged in front of the lens 92 on the optical pathto control the exposure.

The lens 92 refracts incident light to form an object image on the pixelarray (image sensing plane) of the image sensing apparatus 100.

The stop 93 is interposed between the lens 92 and the image sensingapparatus 100 on the optical path, and adjusts the quantity of lightguided to the image sensing apparatus 100 after passing through the lens92.

The image sensing apparatus 100 converts the object image formed on thepixel array 10 into an image signal. The image sensing apparatus 100reads out the image signal from the pixel array 10, and outputs it.

The sensed signal processing circuit 95 is connected to the imagesensing apparatus 100, and processes the image signal output from theimage sensing apparatus 100.

The A/D converter 96 is connected to the sensed signal processingcircuit 95, and converts the processed image signal (analog signal)output from the sensed signal processing circuit 95 into a digitalsignal.

The image signal processor 97 is connected to the A/D converter 96, andperforms various arithmetic processes such as correction for the imagesignal (digital signal) output from the A/D converter 96, generatingimage data. The image signal processor 97 supplies the image data to thememory 87, external I/F 89, overall control/arithmetic unit 99,recording medium control I/F 94, and the like.

The memory 87 is connected to the image signal processor 97, and storesimage data output from the image signal processor 97.

The external I/F 89 is connected to the image signal processor 97. Theexternal I/F 89 transfers image data output from the image signalprocessor 97 to an external device (e.g., a personal computer) via theexternal I/F 89.

The timing generator 98 is connected to the image sensing apparatus 100,sensed signal processing circuit 95, A/D converter 96, and image signalprocessor 97. The timing generator 98 supplies timing signals to theimage sensing apparatus 100, sensed signal processing circuit 95, A/Dconverter 96, and image signal processor 97. The image sensing apparatus100, sensed signal processing circuit 95, A/D converter 96, and imagesignal processor 97 operate in synchronism with the timing signals.

The overall control/arithmetic unit 99 is connected to the timinggenerator 98, image signal processor 97, and recording medium controlI/F 94, and controls all of them.

The recording medium 88 is detachably connected to the recording mediumcontrol I/F 94. The recording medium 88 records image data output fromthe image signal processor 97 via the recording medium control I/F 94.

In this arrangement, if the image sensing apparatus 100 can obtain ahigh-quality image signal, a high-quality image (image data) can beprovided.

An image sensing apparatus 200 according to the second embodiment of thepresent invention will be described with reference to FIGS. 6 to 9. FIG.6 is a view of the arrangement of the image sensing apparatus 200according to the second embodiment of the present invention. FIG. 7 is aview for explaining a readout region RR201 in an effective pixel region03. FIG. 8 is a circuit diagram of a horizontal shift register unit.FIG. 9 is a timing chart showing the detailed operation of a scanningunit 230. Differences from the first embodiment will be mainlyexplained, and a description of the same parts will not be repeated.

The image sensing apparatus 200 is different from the image sensingapparatus 100 in the first embodiment in that the image sensingapparatus 200 comprises the scanning unit 230. The scanning unit 230includes a horizontal shift register unit 204 and vertical shiftregister unit 207.

The horizontal shift register unit 204 includes a second horizontalscanning circuit 206. In accordance with selection signals psel1, psel2,and psel3, the second horizontal scanning circuit 206 can start scanningthe effective pixel region 03 for each of pixel blocks BLK1, BLK4, BLK7,BLK2, BLK5, BLK8, BLK3, BLK6, and BLK9 including a plurality of pixels.

The vertical shift register unit 207 includes a second vertical scanningcircuit 209. In accordance with selection signals pvsel1, pvsel2, andpvsel3, the second vertical scanning circuit 209 can start scanning theeffective pixel region 03 for each of the pixel blocks BLK1 to BLK3,BLK4 to BLK6, and BLK7 to BLK9 including a plurality of pixels.

Although the horizontal shift register unit 204 will be mainlyexplained, the following description also applies to the vertical shiftregister unit 207.

The second horizontal scanning circuit 206 of the horizontal shiftregister unit 204 includes a second shift register 232, a plurality ofsignal lines SL1, SL2, SL3, SL4, SL5, SL6, . . . , and a plurality ofselection circuits 61 a, 61 b, and 61 c.

The second shift register 232 includes a plurality of circuit blocks 232a, 232 b, and 232 c which receive the second start signal hst and scanthe effective pixel region 03 for each pixel block including a pluralityof pixels. The circuit blocks 232 a, 232 b, and 232 c include threeflip-flops 54 to 56, three flip-flops 57 to 59, . . . , respectively.

The plurality of selection circuits 61 a, 61 b, and 61 c arerespectively arranged on the input sides of the plurality of circuitblocks 232 a, 232 b, and 232 c. When the plurality of selection circuits61 a, 61 b, and 61 c are selected by the selection signals psel1, psel2,and psel3, they supply the second start signal hst to the subsequentcircuit blocks 232 a, 232 b, and 232 c, respectively. When the pluralityof selection circuits 61 a, 61 b, and 61 c are not selected by theselection signals psel1, psel2, and psel3, they transfer input signalsto the subsequent circuit blocks 232 a, 232 b, and 232 c, respectively.

The detailed operation of the scanning unit 230 is different from thatin the first embodiment in the following operation, as shown in FIG. 9.

At timing T201, only the selection circuit 61 b receives an activeselection signal psel2, whereas the remaining selection circuits 61 aand 61 c receive inactive selection signals psel1 and psel3. Thus, thesecond shift register 232 selects the circuit block 232 b from aplurality of circuit blocks. From this timing, the first period TP201starts.

At timing T203, the plurality of selection circuits 61 a, 61 b, and 61 creceive the second start signal hst.

At timing T204, since the selection circuit 61 b has received the activeselection signal psel2 and has been selected by the selection signal, itsupplies the second start signal hst to the subsequent circuit block 232b. The circuit block 232 b starts shifting the second start signal hst.That is, the second shift register 232 causes the selected circuit block232 b to start shifting the second start signal hst.

Note that the following operation is the same as that in the firstembodiment. Even if an output from the first stage of the selectedcircuit block 232 b is active (as indicated by a broken line), an enablecircuit 20 keeps the plurality of signal lines SL1, SL2, SL3, SL4, SL5,SL6, . . . disabled, so the horizontal scan signal h4 corresponding tothe fourth column of the effective pixel region 03 does not becomeactive. That is, the second shift register 232 skips the fourth columnof the effective pixel region 03.

At timing T205, the second shift register 232 causes the selectedcircuit block 232 b to shift the second start signal hst by one stage.At this time, since an output from the second stage of the selectedcircuit block 232 b is active and the enable circuit 20 has enabled theplurality of signal lines SL1, SL2, SL3, SL4, SL5, SL6, . . . , thehorizontal scan signal h5 corresponding to the fifth column of theeffective pixel region 03 becomes active. That is, the second shiftregister 232 causes the selected circuit block 232 b to start scanningthe readout region RR1. The first period TP201 ends at this timing, andthe second period TP202 starts from this timing.

At timing T206, the second shift register 232 causes the selectedcircuit block 232 b to shift the second start signal hst by one stage.At this time, since an output from the third stage of the selectedcircuit block 232 b is active and the enable circuit 20 has enabled theplurality of signal lines SL1, SL2, SL3, SL4, SL5, SL6, . . . , thehorizontal scan signal h6 corresponding to the sixth column of theeffective pixel region 03 becomes active.

Since the selection circuit 61 c receives an inactive selection signalpsel3 and is not selected by the selection signal, it transfers theinput signal (second start signal hst) to the subsequent circuit block232 c.

At timing T207, the first shift register 31, the circuit blocks 232 a to232 c of the second shift register 232, and the enable circuit 20receive an active reset signal hrst and are reset. Upon the reset, thecircuit block 232 c ends the shift operation of the second start signalhst. The remaining operation is the same as the operation at timing T7shown in FIG. 4.

As described above, the selected circuit block 232 b receives the secondstart signal hst in the first period TP201 at a timing (e.g., timingT203 shown in FIG. 9) to start scanning the readout region RR201 fromthe start of the second period TP202. Even if a decoder circuit forselecting one of flip-flops which build the shift register is notarranged, the period until scanning of the readout region RR201 startsfor each pixel in the effective pixel region 03 after the end ofscanning the OB region 02 can be shortened. Therefore, the period untilscanning of the readout region starts for each pixel in the effectivepixel region after the end of scanning the optical black region can beshortened by a simple arrangement.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-276758, filed Oct. 24, 2007 which is hereby incorporated byreference herein in its entirety.

1. An image sensing apparatus comprising: a pixel array including anoptical black region and an effective pixel region; and a scanning unitwhich scans the pixel array, the scanning unit including: a first shiftregister which scans the optical black region by a shift operation; anda second shift register which scans the effective pixel region by ashift operation, wherein the second shift register starts the shiftoperation during a first period when the first shift register scans theoptical black region, and scans a readout region serving as a partialregion of the effective pixel region during a second period followingthe first period.
 2. The apparatus according to claim 1, wherein thesecond shift register starts the shift operation in the first period ata timing to start scanning the readout region from the start of thesecond period.
 3. The apparatus according to claim 1, wherein thescanning unit further includes a plurality of signal lines which connectthe second shift register to the pixel array, and an enable circuitwhich disables the plurality of signal lines during the first period andenables the plurality of signal lines during the second period, and thefirst shift register controls the enable circuit to enable the pluralityof signal lines in response to an end of scanning the optical blackregion.
 4. An image sensing apparatus comprising: a pixel arrayincluding an optical black region and an effective pixel region; and ascanning unit which scans the pixel array, the scanning unit including:a first shift register which scans the optical black region by a shiftoperation; and a second shift register which scans the effective pixelregion by a shift operation, wherein the second shift register includesa plurality of circuit blocks which receive a second start signal andscan the effective pixel region for each pixel block including aplurality of pixels, and the second shift register selects one of theplurality of circuit blocks and causes the selected circuit block tostart the shift operation during a first period when the first shiftregister scans the optical black region, and causes the selected circuitblock to start scanning a readout region serving as a partial region ofthe effective pixel region during a second period following the firstperiod.
 5. The apparatus according to claim 4, wherein the second shiftregister causes the selected circuit block to start the shift operationin the first period at a timing to start scanning the readout regionfrom the start of the second period.
 6. The apparatus according to claim4, wherein the scanning unit further includes a plurality of selectioncircuits which are respectively arranged on input sides of thecorresponding circuit blocks, and when selected, supply the second startsignal to subsequent circuit blocks, and when not selected, transferinput signals to the subsequent circuit blocks, a plurality of signallines which connect the plurality of circuit blocks to the pixel array,and an enable circuit which disables the plurality of signal linesduring the first period and enables the plurality of signal lines duringthe second period, and the first shift register controls the enablecircuit to enable the plurality of signal lines in response to an end ofscanning the optical black region.
 7. An imaging system comprising: animage sensing apparatus defined in claim 1; an optical system whichforms an image on an image sensing plane of the image sensing apparatus;and a signal processing unit which processes a signal output from theimage sensing apparatus to generate image data.
 8. An imaging systemcomprising: an image sensing apparatus defined in claim 4; an opticalsystem which forms an image on an image sensing plane of the imagesensing apparatus; and a signal processing unit which processes a signaloutput from the image sensing apparatus to generate image data.
 9. Amethod of driving an image sensing apparatus having a pixel arrayincluding an optical black region and an effective pixel region, and ascanning unit including a first shift register which receives a firststart signal and scans the optical black region by a shift operation ofthe first start signal, and a second shift register which receives asecond start signal and scans the effective pixel region by a shiftoperation of the second start signal, the method comprising: a firststep of causing the first shift register to scan the optical blackregion during a first period; a second step of causing the second shiftregister to start the shift operation during the first period; and athird step of causing the second shift register to scan a readout regionserving as a partial region of the effective pixel region during asecond period following the first period.
 10. The method according toclaim 9, wherein in the first step, the second shift register starts theshift operation in the first period at a timing to start scanning thereadout region from the start of the second period.
 11. A method ofdriving an image sensing apparatus having a pixel array including anoptical black region and an effective pixel region, and a scanning unitincluding a first shift register which scans the optical black region bya shift operation, and a second shift register which scans the effectivepixel region by a shift operation, the second shift register including aplurality of circuit blocks which receive a second start signal and scanthe effective pixel region for each pixel block including a plurality ofpixels, the method comprising: a first step of causing the first shiftregister to scan the optical black region during a first period; asecond step of causing the second shift register to select one of theplurality of circuit blocks and cause the selected circuit block tostart the shift operation during the first period; and a third step ofcausing the second shift register to cause the selected circuit block tostart scanning a readout region serving as a partial region of theeffective pixel region during a second period following the firstperiod.
 12. The method according to claim 11, wherein in the first step,the second shift register causes the selected circuit block to start theshift operation in the first period at a timing to start scanning thereadout region from the start of the second period.